The present invention concerns an improved process for preparing 3-(3-chloro-1H-pyrazol-1-yl)pyridine.
US 20130288893(A1) describes, inter alia, certain (3-halo-1-(pyridin-3-yl)-1H-pyrazol-4-yl)amides and carbamates and their use as pesticides. The route to prepare such compounds involved the preparation of 3-(3-chloro-1H-pyrazol-1-yl)pyridine by the direct coupling of 3-bromopyridine with 3-chloropyrazole. The 3-chloropyrazole was prepared by a) treating 1H-pyrazole with 2-dimethylsulfamoyl chloride and sodium hydride to provide N,N-dimethyl-1H-pyrazole-1-sulfonamide, b) treating the N,N-dimethyl-1H-pyrazole-1-sulfonamide with perchloroethane and n-butyl lithium to provide 3-chloro-N,N-dimethyl-1H-pyrazole-1-sulfonamide, and c) removing the N,N-dimethylsulfonamide from 3-chloro-N,N-dimethyl-1H-pyrazole-1-sulfonamide with trifluoroacetic acid to give the 3-chloropyrazole.
The disclosed process produces low yields, relies on a starting material that is difficult to prepare (3-chloropyrazole) and provides a product that is difficult to isolate in a pure form. It would be desirable to have a process for preparing 3-(3-chloro-1H-pyrazol-1-yl)pyridine (5b) that avoids these problems.